The present invention relates to a variable attenuator for use as a volume control in a sound reproduction system or the like which provides low impedance and high attenuation.
Variable attenuators of the type to which the present invention is an improvement are used in sound reproduction systems and the like as volume controls. Due to the audio response characteristics of the human ear, the variable attenuator is designed to provide a logarithmic attenuation curve with respect to the position of the control member. It has heretofore been unknown in the art to provide a variable attenuator with low impedance and attenuation greater than -20db to -40db without a complicated and expensive configuration.
One method of constructing a variable attenuator with a maximum attenuation approaching -60db is to increase the impedance, thereby creating problems in matching the variable attenuator to the other components of the sound system. Another method involves the use of two or more variable resistors ganged together. However, the noise generated by the sliders of the variable resistors and the inaccuracy in tracking between the two variable resistors due to manufacturing tolerances make this method unsatisfactory.
It is also known to fabricate the resistance element of a variable attenuator in a series of overlapping layers of different resistivity or specific resistance. The generation of noise in such a configuration due to the movement of the slider over the interfaces of the layers in addition to the manufacturing cost and inaccuracy due to manufacturing tolerance in fabricating the layers of different resistivity render this method less than satisfactory.
Still another expedient has been to provide compensating resistors of different resistivity outboard of a main resistance element. The same drawbacks of high manufacturing cost and inaccuracy also limit the desirability of this system.